Chapter 5 Introducing SDN Control in MPLS Networks - High ...

185all upgraded at the same time. Most often there is a mix of older and newer equipment.And from our talks with carriers † , it is a real concern that the older ones cannot keep up.Consider this cycle –the carrier would have a need for new network functionality; theywould approach router vendors to come-up with a solution; router-vendors wouldupgrade router-software (and sometimes change the protocols); upgraded software wouldin-turn increase CPU load; older routers/CPU cards would find it difficult to keep up;ultimately requiring an upgrade in router hardware.SDN reduces switch CPU load by eliminating the need for many of these protocols.All current-distributed-protocol functionally can be replaced by a combination ofnetwork-applications, global-view and switch-API (OpenFlow). Furthermore, aController built on multiple-commodity servers can have much more CPU computationalpower that any one router. And in an SDN based network, when a carrier has a need fornew network functionality, it need not result in upgrading switch-software or changingthe switch-API. Our implementation of traffic-engineering functionality (in Sec. 5.3) isthe perfect example of introducing new network functionality, simply by changing/creating network-applications on top of the map-abstraction.Extensibility: The map-abstraction not only makes writing control-applicationssimpler, it also makes it easier to introduce new functionality into the network. Such newfunctionality could mean new applications or changes to existing applications.Importantly, it does not involve changes to the state-distribution mechanisms. The latteris solved once, and abstracted away from the control programs.This is obviously not the case in today’s IP/MPLS networks, where network functionsare implemented as distributed applications, and each-function ends up using its ownstate-distribution mechanism (Fig. 5.6). Consider the path for introducing newfunctionality in the network today: First the carrier would have a need; then it would haveto ask vendors to implement a solution; vendors would take considerable time to come upwith pre-standard solutions that don’t interoperate; then they would debate in thestandards bodies to come up with an interoperable solution; the vendors then may or may† Google and Global-Crossing.